Conventionally, techniques for recovering CO2 from a CO2-containing exhaust gas, such as a coal flue gas, have been studied (see Patent Literature 1 and Non-Patent Literature 1, for example). Non-Patent Literature 1 describes a CO2 recovery plant adopting a physical adsorption technique and a circulating moving bed regeneration process. The CO2 recovery plant uses a solid adsorbing agent to selectively separate CO2 from a coal flue gas, and recovers the separated CO2.
FIG. 9 shows a schematic configuration of the CO2 recovery plant shown in FIG. 1 of Non-Patent Literature 1. The CO2 recovery plant includes: a cooling tower, an adsorption reactor, a concentration tower, a desorption reactor, and a storage tank, which are vertically arranged in series; and a bucket elevator, which carries the adsorbing agent from the storage tank to the cooling tower. The adsorption reactor, the cooling tower, the desorption reactor, and the storage tank are each packed with zeolite serving as the adsorbing agent. The adsorbing agent sequentially moves from the uppermost cooling tower to the lowermost storage tank, and is carried from the lowermost storage tank to the uppermost cooling tower by the bucket elevator. These chambers and the tank are provided with valves at their lower parts. By opening and closing these valves, a plurality of batches of the adsorbing agent are moved one by one to a lower chamber or tank.
In the CO2 recovery plant with the above configuration, in a pretreatment process using a cooling device and a dehumidifier, water is removed from the coal flue gas by an exhaust gas blower. Then, the coal flue gas is continuously introduced into a lower part of the adsorption reactor. CO2 in the exhaust (flue) gas is adsorbed by the adsorbing agent as moving upward within the adsorption reactor, and the resulting off gas from which CO2 has been removed is discharged to the outside of the system from the top of the adsorption reactor. In the concentration tower, from the adsorbing agent that has adsorbed CO2, part of the CO2 is recovered and compressed together with nitrogen and the like adsorbed by the adsorbing agent. The compressed gas is discharged from the concentration tower, and recovered as a product gas. In the desorption reactor, by feeding of heating steam and decompression, CO2 is caused to desorb from the adsorbing agent. The CO2 that has desorbed is recovered as a product gas. The adsorbing agent thus regenerated is sent to the cooling tower through the storage tank and the bucket elevator. After the adsorbing agent is cooled down, the adsorbing agent is returned to the adsorption reactor and reused.